The invention relates to filters for removing microorganisms from liquid, methods for removing microorganisms from liquid, and methods for manufacturing filters. In particular, the invention relates to filter technology for the removal of bacteria and viruses from drinking water under conditions encountered in faucet mounted filters and pour through filters.
Many filter designs are available for removing contaminants from drinking water. Exemplary designs are described by U.S. Pat. Nos. 5,709,794 to Emmons, et al.; 5,536,394 to Lund, et al.; 5,525,214 to Hembree; 5,106,500 to Hembree, et al.; and 5,268,093 to Hembree, et al. which were originally assigned to Recovery Engineering, Inc.
Several filter designs utilizing membrane technology have been proposed for removing submicron size microorganisms. For example, U.S. Pat. No. 5,017,292 to DiLeo, et al. describes a composite membrane including a porous membrane substrate, a surface skin having ultrafiltration separation properties, and an intermediate porous zone having an average pore size smaller than that of the substrate.
Chemical forces can be used to adhere microbials to solid surfaces. See Bitton and Marshall, xe2x80x9cAdsorption of Micro organisms to Surfaces,xe2x80x9d John Wiley and Sons, New York, pages 1-57 and by Gerba C.P., xe2x80x9cApplied and Theoretical Aspects of Virus Adsorption to Surfaces,xe2x80x9d Adv. Appl. Microbiol., vol. 30, pages 133-168 (1984). According to their discussion, charge interaction can be considered a major cause of interaction between virus and adsorbent surfaces. Most viruses have coats composed of protein polypeptides containing amino acids such as glutamic acid, aspartic acid, histidine and tyrosine. These amino acids contain carboxyl and amino groups which, upon ionization, give the viral capsid an electrical charge.
Based on the theory of charge interaction as means of removing micro organisms from the water, positively charged ion exchange resins have been utilized for bacteria adsorption by Daniels, xe2x80x9cDevelopments In Industrial Microbiologyxe2x80x9d, Vol. 13; Proceedings of the twenty-eighth General Meeting of the Society for Industrial Microbiology, pages 211-243 (1972). The fundamental framework of these ion exchange resins is an elastic three dimensional hydrocarbon network comprising ionizable groups, either cationic or anionic, chemically bonded to the backbone of a hydrocarbon framework. The network is normally fixed, insoluble in common solvents and chemically inert. The ionizable functional groups attached to the matrix carry active ions with counter-ions which can be exchanged by the other counter-ions existed in water. Typical examples of commercially available ion exchange resins are the poly styrene cross-linked with divinyl benzene (DVB), and the methacrylate copolymerized with DVB. In the case of polystyrene, a three dimensional network is formed first, and the functional groups are then introduced into benzene rings through chloromethylation. Since those ionizable groups are highly hydrophilic, the more the existence of those groups in resin structure, the more the resin will swell to restrict the flow of water. The resistance to flow exhibited by these resins in controlled by the degree of cross-linking usually in the range of 2 to 12% as discussed by K. Dorfner, xe2x80x9cIon Exchangersxe2x80x9d Ann Arbor Science Publishers, Inc., pages 16-35, New York (1962). With a low degree of cross-linking, the hydrocarbon network is more easily stretched, the swelling is large, and the resin exchanges small ions rapidly and even permits relatively large ions to undergo exchange. Conversely, as the cross-linking is increased to make the structure more rigid for high liquid flow, the hydrocarbon matrix is less resilient, the pores in the resin network are narrowed, the exchange process is slower, and the exchanger resin increases its tendency to exclude large ions from entering the structure. The ion exchange resins made by cross-linking the functional group carrying polymers have been successfully applied for the removal of both organic and inorganic ions in Angstrom size range but they are normally unsuitable for the relatively large sized micro-organisms. Also, the matrix swells and the flow resistance increases due to the pore narrowing.
U.S. Pat. No. 4,361,486 to Hou, et al., describes a filter which can be used for removing soluble iron and manganese from an aqueous fluid, and for removing and inactivating microorganisms from fluids. The filter includes an amount of particulate including magnesium peroxide or calcium peroxide immobilized on a substantially inert porous matrix. The filter media can be provided with an electropositive potential by modifying the surface of the particulate or inert porous matrix with a surface modifying agent. Hou, et al., xe2x80x9cCapture of Latex Beads, Bacteria, Endotoxin, and Viruses by Charge-Modified Filters,xe2x80x9d Appl. Environ. Microbiol., vol. 40, no. 5, pages 892-896, November 1980, reports the use of electropositive filters in removing microorganisms and other negatively charged particles from water. Charge modified filters are disclosed by U.S. Pat. Nos. 4,305,782 and 4,473,474 Ostreicher, et al.
U.S. Pat. No. 4,352,884 to Nakashima, et al. discloses a carrier for bioactive materials comprised of a substrate coated with a copolymer. The substrate may be one of various materials, including inorganic nature such as glass, activated carbon, silica, and alumina as well as organic polymers such as polystyrene, polyethylene, polyvinyl chloride, nylon, polyester, polymethyl methacrylate, and naturally occurring high polymers such as cellulose. The copolymer can be an acrylate or methacrylate monomer and a copolymerizable unsaturated carboxylic acid or unsaturated amine.
U.S. Pat. No. 3,898,188 to Rembawn, et al. and U.S. Pat. No. 3,784,649 to Buckman, et al. describe the polymerization of a dihalide and a ditertiary amine to form poly-quaternary ammonium resin. These polymers have found utility as flocculants in the clarification of water supplies. The materials are also known to exhibit germicidal action or as an effective bactericidal and fungicidal agents.
Preston, D. R., et al., xe2x80x9cRemoval of Viruses from Tapwater by Fiberglass Filters Modified with a Combination of Cationic Polymers,xe2x80x9d Wat. Sci. Tech. Vol. 21, No. 3, pp 93-98 (1989) describes the development of an electropositive filter capable of adsorbing enteroviruses from water at pH 5 to 9. This article reports that electronegative fiberglass filters can be converted to electropositive filters by soaking the filters in an aqueous solution of a cationic polymer and allowing the treated filters to air dry. The cationic polymers polyethylenimine and Nalco cationic polymer 7111 can be used to produce a filter which can recover enteroviruses from environmental waters.
Faucet-mounted drinking water filters are described by U.S. Pat. No. 5,525,214. In general, faucet-mounted drinking filters include a filtration media for removing chemical and mineral contaminants as well as larger microorganisms. Common filter media include carbon, which is often in the form of a porous block. Additional contaminants, such as lead, can be removed with the addition of selective adsorbents. In addition, the filtration media commonly used in faucet-mounted drinking water filters have been combined with microfilters for the removal of small microorganisms and particles. The microfiltration is usually accomplished as a result of the fine porosity of the carbon block, or with the use of a second filter, including a hollow fiber membrane material.
A filter for removing microorganisms from a liquid is provided by the invention. The filter includes a microorganism filtration media including a substrate having a reactive surface and a polymer covalently bonded to the reactive surface of the substrate. The polymer includes a plurality of cationic groups for attracting microorganisms in a liquid. The filtration media exhibits an MS-2 virus removal coefficient in water of greater than 10 ml/g-sec.
The polymer which is covalently bonded to the substrate is preferably at least one of polyamide-polyamine polymer, polyamine polymer, and mixtures thereof. Exemplary polyamine and polyamide-polyamine polymers include those polymers having at least one of the following repeating units: 
wherein n, for each of formulas I-III, is between about 10 and 100,000. The polymer preferably has a number average molecular weight of between about 25,000 and about 2,000,000, and more preferably between about 500,000 and 1,500,000. The polymer can be provided as a mixture of separate polymers including repeating units of any one or more of formulas I-III, or as copolymers containing repeating units of any one of formulas I-III or any combination of formulas I-III. Another polymer can include a reaction product of polyethylenimine and a cross-linking agent, such as, a di-epoxy cross-linking agent. The polyethylenimine polymer preferably has a repeating unit of the following formula:
"Parenopenst"CH2xe2x80x94CH2xe2x80x94NH"Parenclosest"nxe2x80x83xe2x80x83IV
wherein n is between about 10 and about 1,000,000. The polyethylenimine polymer preferably has a number average molecular weight of between about 800 and about 1,000,000. The di-epoxy cross-linking agent is preferably a diglycidyl ether such as the diglycidyl ether of 1,4-butanediol.
Substrate is preferably a substrate having a surface which is capable of reacting with the polymer to provide a covalent bond between the substrate and the polymer. Preferably, the reactive surface of the substrate includes functional groups capable of reacting with reactive groups of the polymer, including epoxy groups and azetidinium groups. Exemplary functional groups which can be present on the substrate include hydroxyl groups, amino groups and hydrosulfyl groups. The substrate can be provided in the form of a fibrous material and/or particulate material. Preferred materials include glass, silica (including diatomaceous earth), alumina, polystyrene, polypropylene, polyethylene, polyvinyl alcohol, polyamide, cellulose, and mixtures thereof. A preferred substrate includes glass fiber web.
The filtration media includes a charge density of at least about 0.001 milli-equivalent/gram filtration media. In addition, the filtration media preferably exhibits an extractables of less than 20 ppm nitrogen in extracted water, wherein the extractables is determined by a Hach DR-700 colorimeter after soaking two grams of filtration media into 250 ml nitrogen free water for two hours at room temperature.
A method for removing microorganisms from water is provided by the invention. The method includes a step of reacting a polymer to a substrate surface to provide a filtration media exhibiting covalent bonding between the polymer and the substrate surface. The polymer includes a plurality of cationic groups for attracting microorganisms, and the filtration media exhibits an MS-2 virus removal coefficient in water of greater than 10 ml/g-sec. The method includes a step of passing water through the filtration media to remove microorganisms from the water.
A faucet mount filter is provided by the invention. The faucet mount filter includes a housing having an inlet, an outlet, and an interior region. The interior region contains a water treatment material. The water treatment material includes a filtration media having a substrate with a reactive surface and a polymer covalently bonded to the reactive surface of the substrate. The polymer includes a plurality of cationic groups for attracting microorganisms. The faucet mount filter includes a valve for controlling flow of water into the inlet of the housing, and an adapter for attaching the valve to a faucet.
A pour through filter is provided by the invention. The pour through filter includes a housing having an inlet, an outlet, and an interior region. The interior region includes a pleated filtration media. The pleated filtration media includes a substrate having a reactive surface and a polymer covalently bonded to the reactive surface. In addition, the polymer includes a plurality of cationic groups for attracting microorganisms in water. The interior region can additionally include a layer of microorganism filtration media in combination with the pleated microorganism filtration media. For example, the layer of microorganism filtration media can be provided around the pleated microorganism filtration media.
A method for manufacturing a microorganism filtration media is provided by the invention. The method includes steps of providing a substrate, such as, as glass fiber web, coating the substrate with a polymer, and heating the coated substrate to dry and covalently react the polymer to the substrate. The polymer is preferably at least one of polyamide-polyamine polymer, polyamine polymer, and mixtures thereof, and is preferably provided at a solids content of between about 0.1 wt. % and about 10 wt. %.